Identification of vascular endothelial growth factor determinants for binding KDR and FLT-1 receptors. Generation of receptor-selective VEGF variants by site-directed mutagenesis

VEGF165 modulates proliferation, adhesion, migration and differentiation of cultured human outer root sheath cells from central hair follicle epithelium through VEGFR-2 activation in vitro

BACKGROUND

The functional state of vasculature is tightly controlled by vascular endothelial growth factor receptor-2 (VEGFR-2). Recent studies revealed that VEGFR-2 is expressed on hair follicle keratinocytes.

OBJECTIVE

We proposed to investigate its effect on proliferation, adhesion and migration of cultured human outer root sheath cells from central hair follicle epithelium.

METHODS

These studies were undertaken in vitro using human outer root sheath cells from central hair follicle epithelium, immunohistochemistry analysis, immunofluorescence microscopy, western blot analysis, MTT, trans well analysis, and RT-PCR.

RESULTS

Our results show that VEGFR-2 is expressed in these cells in vivo and in vitro. Furthermore, proliferation and migration of cultured human outer root sheath cells from central hair follicle epithelium is increased by VEGF165, while homotypic adhesion is decreased but heterotypic adhesion is increased. VEGF165 upregulates integrin β1 but dowregulates lgr6 expression. In addition, phosphorylation of VEGFR-2, Erk1/2, c-Jun and p38, are increased following VEGF165 treatment and these effects are reversed by a VEGFR-2 neutralizing antibody.

CONCLUSION

Our results suggest a role of VEGF/VEGFR-2 beyond angiogenesis in hair follicle regulation.

The impact of the receptor binding profiles of the vascular endothelial growth factors on their angiogenic features

BACKGROUND

Vascular endothelial growth factors (VEGFs) are potential therapeutic agents for treatment of ischemic diseases. Their angiogenic effects are mainly mediated through VEGF receptor 2 (VEGFR2).

METHODS

Receptor binding, signaling, and biological efficacy of several VEGFR2 ligands were compared to determine their characteristics regarding angiogenic activity and vascular permeability.

RESULTS

Tested VEGFR2 ligands induced receptor tyrosine phosphorylation with different efficacy depending on their binding affinities. However, the tyrosine phosphorylation pattern and the activation of the major downstream signaling pathways were comparable. The maximal angiogenic effect stimulated by different VEGFR2 ligands was dependent on their ability to bind to co-receptor Neuropilin (Nrp), which was shown to form complexes with VEGFR2. The ability of these VEGFR2 ligands to induce vascular permeability was dependent on their concentration and VEGFR2 affinity, but not on Nrp binding.

CONCLUSIONS

VEGFR2 activation alone is sufficient for inducing endothelial cell proliferation, formation of tube-like structures and vascular permeability. The level of VEGFR2 activation is dependent on the binding properties of the ligand used. However, closely similar activation pattern of the receptor kinase domain is seen with all VEGFR2 ligands. Nrp binding strengthens the angiogenic potency without increasing vascular permeability.

GENERAL SIGNIFICANCE

This study sheds light on how different structurally closely related VEGFR2 ligands bind to and signal via VEGFR2/Nrp complex to induce angiogenesis and vascular permeability. The knowledge of this study could be used for designing VEGFR2/Nrp ligands with improved therapeutic properties.

VEGFR and type-V RTK activation and signaling

Vascular endothelial growth factor receptors (VEGFRs) in vertebrates play essential roles in the regulation of angiogenesis and lymphangiogenesis. VEGFRs belong to the receptor-type tyrosine kinase (RTK) supergene family. They consist of a ligand-binding region with seven immunoglobulin (7 Ig) -like domains, a trans-membrane (TM) domain, and a tyrosine kinase (TK) domain with a long kinase insert (KI) (also known as a type-V RTK). Structurally, VEGFRs are distantly related to the members of the M-colony stimulating factor receptor/platelet-derived growth factor receptor (CSFR)/(PDGFR) family, which have five immunoglobulin (5 Ig)-like domains. However, signal transduction in VEGFRs significantly differs from that in M-CSFR/PDGFRs. VEGFR2, the major signal transducer for angiogenesis, preferentially uses the phospholipase Cγ-protein kinase C (PLC-γ-PKC)-MAPK pathway, whereas M-CSFR/PDGFRs use the PI3 kinase-Ras-MAPK pathway for cell proliferation. In phylogenetic development, the VEGFR-like receptor in nonvertebrates appears to be the ancestor of the 7 Ig- and 5 Ig-RTK families because most nonvertebrates have only a single 7 Ig-RTK gene. In mammals, VEGFRs are deeply involved in pathological angiogenesis, including cancer and inflammation. Thus, an efficient inhibitor targeting VEGFRs could be useful in suppressing various diseases.

Vascular contributions to early ovarian development: potential roles of VEGFA isoforms

Vascularisation is an essential component of ovarian morphogenesis; however, little is known regarding factors regulating the establishment of vasculature in the ovary. Angiogenesis involving extensive endothelial cell migration is a critical component of vessel formation in the embryonic testis but vasculogenic mechanisms appear to play a prominent role in ovarian vascularisation. Vasculature has a strong influence on the formation of ovarian structures, and the early developmental processes of ovigerous cord formation, primordial follicle assembly and follicle activation are all initiated in regions of the ovary that are in close association with the highly vascular medulla. The principal angiogenic factor, vascular endothelial growth factor A (VEGFA), has an important role in both endothelial cell differentiation and vascular pattern development. Expression of VEGFA has been localised to ovigerous cords and follicles in developing ovaries and an increased expression of pro-angiogenic Vegfa isoform mRNA in relation to anti-angiogenic isoform mRNA occurs at the same time-point as the peak of primordial follicle assembly in perinatal rats. Elucidation of specific genes that affect vascular development within the ovary may be critical for determining not only the normal mechanisms of ovarian morphogenesis, but also for understanding certain ovarian reproductive disorders.

Navigation rules for vessels and neurons: cooperative signaling between VEGF and neural guidance cues

Many organs, such as lungs, nerves, blood and lymphatic vessels, consist of complex networks that carry flows of information, gases, and nutrients within the body. The morphogenetic patterning that generates these organs involves the coordinated action of developmental signaling cues that guide migration of specialized cells. Precision guidance of endothelial tip cells by vascular endothelial growth factors (VEGFs) is well established, and several families of neural guidance molecules have been identified to exert guidance function in both the nervous and the vascular systems. This review discusses recent advances in VEGF research, focusing on the emerging role of neural guidance molecules as key regulators of VEGF function during vascular development and on the novel role of VEGFs in neural cell migration and nerve wiring.

Opportunities and challenges for successful use of bevacizumab in pediatrics

Bevacizumab (Avastin) has rapidly gained status as a broadly active agent for malignancies of several different histologies in adults. This activity has spawned a range of uses in pediatrics for both oncologic and non-oncologic indications. Early analyses indicate that pediatric cancers exhibit a spectrum of responses to bevacizumab that suggest its activity may be more limited than in adult oncology. Most exciting, is that for low-grade tumors that threaten vision and hearing, there is not only evidence for objective tumor response but for recovery of lost function as well. In addition to oncological indications, there is a range of uses for non-oncologic disease for which bevacizumab has clear activity. Finally, a number of mechanisms have been identified as contributing to bevacizumab resistance in cancer. Elucidating these mechanisms will guide the development of future clinical trials of bevacizumab in pediatric oncology.

Age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly, and the prevalence of the disease increases exponentially with every decade after age 50 years. It is a multifactorial disease involving a complex interplay of genetic, environmental, metabolic, and functional factors. Besides smoking, hypertension, obesity, and certain dietary habits, a growing body of evidence indicates that inflammation and the immune system may play a key role in the development of the disease. AMD may progress from the early form to the intermediate form and then to the advanced form, where two subtypes exist: the nonneovascular (dry) type and the neovascular (wet) type. The results from the Age-Related Eye Disease Study have shown that for the nonneovascular type of AMD, supplementation with high-dose antioxidants (vitamin C, vitamin E, and β-carotene) and zinc is recommended for those with the intermediate form of AMD in one or both eyes or with advanced AMD or vision loss due to AMD in one eye. As for the neovascular type of the advanced AMD, the current standard of therapy is intravitreal injections of vascular endothelial growth factor inhibitors. In addition, lifestyle and dietary modifications including improved physical activity, reduced daily sodium intake, and reduced intake of solid fats, added sugars, cholesterol, and refined grain foods are recommended. To date, no study has demonstrated that AMD can be cured or effectively prevented. Clearly, more research is needed to fully understand the pathophysiology as well as to develop prevention and treatment strategies for this devastating disease.

PTK787/ZK222584 combined with interferon alpha and 5-fluorouracil synergistically inhibits VEGF signaling pathway in hepatocellular carcinoma

BACKGROUND

The prognosis of patients with hepatocellular carcinoma (HCC) and portal vein tumor thrombus remains poor. We previously reported the beneficial effects of interferon alpha (IFN) and 5-fluorouracil (5-FU) combination therapy for these patients. We showed that the mechanism of therapy was regulation of vascular endothelial growth factor (VEGF). Here, we combined IFN/5-FU therapy with the VEGF receptor-selective inhibitor PTK787/ZK222584 (PTK/ZK) and examined the antitumor effects and the mechanism of action.

METHODS

We studied two HCC cell lines, PLC/PRF/5 and HuH7, and a human umbilical vein endothelial cell line, HUVEC. We studied the effects of IFN/5-FU with or without PTK/ZK in growth inhibition assays, immunohistochemistry, Western blot analysis, and immunocytochemistry.

RESULTS

In a HuH7 xenograft model, the combination of PTK/ZK and IFN/5-FU significantly inhibited proliferation, induced apoptosis, decreased microvessel density, reduced the number of tumor cells that expressed VEGF receptor 2 (VEGFR-2), and repressed the phosphorylation of Akt in vivo. In HCC cells and HUVECs in vitro, IFN/5-FU plus PTK/ZK repressed the expression of VEGFR-2 and repressed the phosphorylation of VEGFR, Akt, Erk, and p38MAPK.

CONCLUSIONS

VEGF signaling inhibition enhanced the antitumor effects of IFN/5-FU therapy on HCC cells and endothelial cells via Erk, Akt, and p38MAPK pathways.

Computational Alanine Scanning Mutagenesis: MM-PBSA vs TI

Understanding protein-protein association and being able to determine the crucial residues responsible for their association (hot-spots) is a key issue with huge practical applications such as rational drug design and protein engineering. A variety of computational methods exist to detect hot-spots residues, but the development of a fast and accurate quantitative alanine scanning mutagenesis (ASM) continues to be crucial. Using four protein-protein complexes, we have compared a variation of the standard computational ASM protocol developed at our group, based on the Molecular Mechanics/Poisson-Boltzmann Surface Area (MM-PBSA) approach, against Thermodynamic Integration (TI), a well-known and accurate but computationally expensive method. To compare the efficiency and the accuracy of the two methods, we have calculated the protein-protein binding free energy differences upon alanine mutation of interfacial residues (ΔΔGbind). In relation to the experimental ΔΔGbind values, the average error obtained with TI was 1.53 kcal/mol, while the ASM protocol resulted in an average error of 1.18 kcal/mol. The results demonstrate that the much faster ASM protocol gives results at the same level of accuracy as the TI method but at a fraction of the computational time required to run TI. This ASM protocol is therefore a strong and efficient alternative to the systematic evaluation of protein-protein interfaces, involving hundreds of amino acid residues in search of hot-spots.

Peptide vaccines and targeting HER and VEGF proteins may offer a potentially new paradigm in cancer immunotherapy

The ErbB family (HER-1, HER-2, HER-3 and HER-4) of receptor tyrosine kinases has been the focus of cancer immunotherapeutic strategies while antiangiogenic therapies have focused on VEGF and its receptors VEGFR-1 and VEGFR-2. Agents targeting receptor tyrosine kinases in oncology include therapeutic antibodies to receptor tyrosine kinase ligands or the receptors themselves, and small-molecule inhibitors. Many of the US FDA-approved therapies targeting HER-2 and VEGF exhibit unacceptable toxicities, and show problems of efficacy, development of resistance and unacceptable safety profiles that continue to hamper their clinical progress. The combination of different peptide vaccines and peptidomimetics targeting specific molecular pathways that are dysregulated in tumors may potentiate anticancer immune responses, bypass immune tolerance and circumvent resistance mechanisms. The focus of this review is to discuss efforts in our laboratory spanning two decades of rationally developing peptide vaccines and therapeutics for breast cancer. This review highlights the prospective benefit of a new, untapped category of therapies biologically targeted to EGF receptor (HER-1), HER-2 and VEGF with potential peptide 'blockbusters' that could lay the foundation of a new paradigm in cancer immunotherapy by creating clinical breakthroughs for safe and efficacious cancer cures.

Positron emission tomography imaging of vascular endothelial growth factor receptor expression with (61)Cu-labeled lysine-tagged VEGF121

Overexpression of vascular endothelial growth factor (VEGF) and VEGF receptors (VEGFRs) indicates poor prognosis for cancer patients in a variety of clinical studies. Our goal is to develop a tracer for positron emission tomography (PET) imaging of VEGFR expression using recombinant human VEGF121 with three lysine residues fused to the N-terminus (denoted as K3-VEGF121), which can facilitate radiolabeling without affecting its VEGFR binding affinity. K3-VEGF121 was conjugated with 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) and labeled with (61)Cu (t1/2: 3.3 h; 62% β(+)). The IC50 value of NOTA-K3-VEGF121 for VEGFR-2 was comparable to that of K3-VEGF121 (1.50 and 0.65 nM, respectively) based on a cell binding assay. (61)Cu labeling was achieved with good yield (55 ± 10%) and specific activity (4.2 GBq/mg). Serial PET imaging showed that the 4T1 tumor uptake of (61)Cu-NOTA-K3-VEGF121 was 3.4 ± 0.5, 4.9 ± 1.0, 5.2 ± 1.0, and 4.8 ± 0.8%ID/g (n = 4) at 0.5, 2, 4, and 8 h postinjection, respectively, which was consistent with biodistribution data measured by γ counting. Blocking experiments and ex vivo histology confirmed the VEGFR specificity of (61)Cu-NOTA-K3-VEGF121. Extrapolated human dosimetry calculation showed that liver was the organ with the highest radiation dose. The use of (61)Cu as the radiolabel is desirable for small proteins such as K3-VEGF121, which has a much higher β(+) branching ratio than the commonly used (64)Cu (62% vs 17%), thereby offering stronger signal intensity and lower tracer dose for PET imaging.

Comparison of the use of 5-fluorouracil and bevacizumab in primary trabeculectomy: results at 1 year

BACKGROUND

The present study compared the effects of adjuvant bevacizumab and 5-fluorouracil on the efficacy and safety of trabeculectomy.

DESIGN

A nonrandomized, prospective, interventional case study.

PARTICIPANTS

A total of 62 patients in two groups undergoing primary trabeculectomy.

METHODS

In Group 1 (21 primary open-angle glaucoma, nine pseudoexfoliative glaucoma), trabeculectomy was performed with an adjuvant 5% solution of 5-fluorouracil administered for 4 min, intraoperatively. In Group 2 (21 primary open-angle glaucoma, 11 pseudoexfoliative glaucoma), trabeculectomy was enhanced with 1.25 mg of bevacizumab applied subconjunctivally immediately before and after surgery and again 1 and 7 days after surgery.

MAIN OUTCOME MEASURES

Intraocular pressure, best corrected visual acuity, visual field index, bleb morphology, cornel endothelial cell count.

RESULTS

Mean intraocular pressure was 28.0 ± 8.0 mmHg before 5-fluorouracil-augmented trabeculectomy and 27.8 ± 9.5 mmHg before bevacizumab-augmented trabeculectomy. After 12 months, mean intraocular pressure was 13.6 ± 4.4 mmHg in the 5-fluorouracil group and 14.7 ± 4.7 mmHg in the bevacizumab group. A 30% reduction of initial intraocular pressure was attained in 86.7% of patients in the 5-fluorouracil group and 78.1% of patients in the bevacizumab group at the end of follow up. No significant differences were noted between the two studied groups with respect to corneal endothelial density, visual field indices and postoperative complications.

CONCLUSIONS

The 12-month intraocular pressure results showed no significant differences between the two groups of patients after bevacizumab or 5-fluorouracil to augment trabeculectomy. However, to obtain successful intraocular pressure control more patients in bevacizumab group needed medical therapy.

The discovery of placenta growth factor and its biological activity

Angiogenesis is a complex biological phenomenon crucial for a correct embryonic development and for post-natal growth. In adult life, it is a tightly regulated process confined to the uterus and ovary during the different phases of the menstrual cycle and to the heart and skeletal muscles after prolonged and sustained physical exercise. Conversly, angiogenesis is one of the major pathological changes associated with several complex diseases like cancer, atherosclerosis, arthritis, diabetic retinopathy and age-related macular degeneration. Among the several molecular players involved in angiogenesis, some members of VEGF family, VEGF-A, VEGF-B and placenta growth factor (PlGF), and the related receptors VEGF receptor 1 (VEGFR-1, also known as Flt-1) and VEGF receptor 2 (VEGFR-2, also known as Flk-1 in mice and KDR in human) have a decisive role. In this review, we describe the discovery and molecular characteristics of PlGF, and discuss the biological role of this growth factor in physiological and pathological conditions.

Targeting the proangiogenic VEGF-VEGFR protein-protein interface with drug-like compounds by in silico and in vitro screening

Protein-protein interactions play a central role in medicine, and their modulation with small organic compounds remains an enormous challenge. Because it has been noted that the macromolecular complexes modulated to date have a relatively pronounced binding cavity at the interface, we decided to perform screening experiments over the vascular endothelial growth factor receptor (VEGFR), a validated target for antiangiogenic treatments with a very flat interface. We focused the study on the VEGFR-1 D2 domain, and 20 active compounds were identified. These small compounds contained a (3-carboxy-2-ureido)thiophen unit and had IC(50) values in the low micromolar range. The most potent compound inhibited the VEGF-induced VEGFR-1 transduction pathways. Our findings suggest that our best hit may be a promising scaffold to probe this macromolecular complex and for the development of treatments of VEGFR-1-dependent diseases.

The immunopharmacologic potential of Semaxanib and new generation directed therapeutic drugs: Receptor tyrosine kinase regulation with anti-tumorigenensis/angiogenesis properties

Molecular signaling of messages emanating from cellular membranes through receptor tyrosine kinases (RTKs) is a major mechanism for intercellular communication and transduction during development and metabolism, as well as in disease-associated processes. The phosphorylation status and signaling activity of RTKs are determined by a dynamic equilibrium of the activity of both RTKs and protein tyrosine phosphatases (PTPs). RTKs are essentially a class of cell-surface receptors for growth factors and other extracellular ligands, the most conspicuous perhaps are members of the vascular endothelial growth factor (VEGF) gene family, which plays a fundamental role in the growth and differentiation of vascular, as well as lymphatic endothelial cells. In particular, VEGF is a major regulator of normal (physiologic) and abnormal (cancerous) angiogenesis, including that associated with tumors and cancer. Blockers/inhibitors and regulators of RTKs are indeed promising cancer interventions, their specific mechanisms are yet to be unraveled. In this cutting-edge synopsis, I elaborate on breakthroughs/advances and current concepts of RTK regulation, further shedding light on exploring the role of potential regulators, particularly the RTK inhibitor Semaxanib, and the mechanisms associated with tumorigenesis in an effort to understand a potentially alleviating pharmacologic therapeutic intervention. This survey also tackles the loopholes and shortcomings of the aforementioned inhibitory role of Semaxanib, especially its inefficacy and ultimate discontinuation of relevant clinical trials.

The balance of proangiogenic and antiangiogenic VEGFA isoforms regulate follicle development

Vascular endothelial growth factor A (VEGFA) has been extensively studied because of its role in follicular development and is a principal angiogenic factor essential for angiogenesis. Since vascularization of the theca layer increases as follicles progress in size through preantral and antral stages, VEGFA might influence follicle growth via the regulation of angiogenesis. However, VEGFA might also influence follicular development through nonangiogenic mechanisms, since its expression has been localized in nonvascular follicles and cells. Alternative mRNA splicing of eight exons from the VEGFA gene results in the formation of various VEGFA isoforms. Each isoform has unique properties and is identified by the number of amino acids within the mature protein. Proangiogenic isoforms (VEGFA_XXX) are encoded by exon 8a, whereas a sister set of isoforms (VEGFA_XXXB) with antiangiogenic properties is encoded by exon 8b. The antiangiogenic VEGFA_XXXB isoforms comprise the majority of VEGFA expressed in most tissues, whereas expression of the proangiogenic VEGFA isoforms is upregulated in tissues undergoing active angiogenesis. Although proangiogenic and antiangiogenic isoforms can now be distinguished from one another, many studies evaluating VEGFA in ovarian and follicular development up to now have not differentiated proangiogenic VEGFA from antiangiogenic VEGFA. Experiments from our laboratory indicate that proangiogenic VEGFA promotes follicle recruitment and early follicular development and antiangiogenic VEGFA inhibits these processes. The balance of proangiogenic versus antiangiognic VEGFA isoforms is thus of importance during follicle development. Further studies are warranted to elucidate the way that this balance regulates follicular formation and progression.

Soluble vascular endothelial growth factor decoy receptor FP3 exerts potent antiangiogenic effects

The binding of vascular endothelial growth factor (VEGF) to its receptors stimulates tumor growth; therefore, modulation of VEGF would be a viable approach for antiangiogenic therapy. We constructed a series of soluble decoy receptors containing different VEGF receptor 1 (FLT1) and VEGF receptor 2 (KDR) extracellular domains fused with the Fc region of human immunoglobulin (Ig) and evaluated their antiangiogenic effects and antitumor effects. Results of in vitro binding and cell proliferation assays revealed that decoy receptor FP3 had the highest affinity to VEGF-A and -B. Compared with bevacizumab, FP3 more effectively inhibited human umbilical vein endothelial cell (HUVEC) migration and vessel sprouting from rat aortic rings. FP3 significantly reduced phosphorylation of AKT and ERK1/2, critical proteins in the VEGF-mediated survival pathway in endothelial cells. Moreover, FP3 inhibited tumor growth in human hepatocellular carcinoma (HepG2), breast cancer (MCF-7), and colorectal cancer (LoVo) tumor models, and reduced microvessel density in tumor tissues. The FP3-mediated inhibition of tumor growth was significantly higher than that of bevacizumab at the same dose. FP3 also demonstrated synergistic antitumor effects when combined with 5-fluorouracil (5-FU). Taken together, FP3 shows a high affinity for VEGF and produced antiangiogenic effects, suggesting its potential for treating angiogenesis-related diseases such as cancer.

Effectiveness of ranibizumab intravitreal injections for exudative age-related macular degeneration treatment: 12-month outcomes

Background

The aim of this paper was to evaluate functional and anatomical results of intravitreal ranibizumab injections and the course of exudative age-related macular degeneration (AMD) treatment over a 12-month observation period.

Material/Methods

In 25 patients with active dominantly classic exudative AMD, treatment was performed according to the following schedule: 3 intravitreal injections of 0.5 mg ranibizumab at monthly intervals (saturation phase); further injections were based on activity of the neovascular process. Changes in VA and central retinal thickness (CRT) during treatment were evaluated with ANOVA testing.

Results

Mean pre-treatment best corrected visual acuity was 0.73±0.27 logMAR. After the third ranibizumab injection the best results, 0.54±0.27 logMAR, were seen; 12-month results were 0.58±0.26 logMAR. Patients had a mean improvement of 10.6 letters at 12 months. In 92% of patients stabilization or improvement of vision was observed. The mean number of injections in the 12-month period was 6.

Baseline mean CRT was 351.12±74.15 μm. After the first ranibizumab injection it decreased significantly to 221.96±60.85 μm, after the third injection it was 200.80±47.63 μm, and after 12 months it was 213.16±44.37 μm. Mean correlations between baseline average CRT and baseline average VA measured in ETDRS letters (p=0.017) and in logMAR scale (p=0.033) and between average CRT after the third injection and average VA in logMAR scale after the third injection (p=0.047) were noted.

Conclusions

Treatment with intravitreal ranibizumab injections according to the presented scheme provides AMD patients with a chance of stabilization and improvement of the topical state, with a lower number of injections and preserved topical and general safety. Our results suggest that regular monthly controls are necessary to be able react rapidly to the smallest signs of deterioration, not only in visual acuity, but also in OCT images.

Development of Anti-VEGF Therapies for Intraocular Use: A Guide for Clinicians

Angiogenesis is the process by which new blood vessels form from existing vessel networks. In the past three decades, significant progress has been made in our understanding of angiogenesis; progress driven in large part by the increasing realization that blood vessel growth can promote or facilitate disease. By the early 1990s, it had become clear that the recently discovered “vascular endothelial growth factor” (VEGF) was a powerful mediator of angiogenesis. As a result, several groups targeted this molecule as a potential mediator of retinal ischemia-induced neovascularization in disorders such as diabetic retinopathy and retinal vein occlusion. Around this time, it also became clear that increased intraocular VEGF production was not limited to ischemic retinal diseases but was also a feature of choroidal vascular diseases such as neovascular age-related macular degeneration (AMD). Thus, a new therapeutic era emerged, utilizing VEGF blockade for the management of chorioretinal diseases characterized by vascular hyperpermeability and/or neovascularization. In this review, we provide a guide for clinicians on the development of anti-VEGF therapies for intraocular use.

Neuropilin-1 expression in cancer and development

Neuropilin (NRP)-1 is a co-receptor for vascular endothelial growth factor (VEGF). Preclinical data suggest that blockade of NRP1 suppresses tumour growth by inhibiting angiogenesis, in addition to directly inhibiting tumour cell proliferation in certain models. A humanized monoclonal antibody to NRP1 is currently being evaluated as a potential anti-cancer therapy in clinical trials. However, the expression of NRP1 in cancer and physiological angiogenesis has yet to be systematically described. Here we characterize the in situ expression of NRP1 in human cancer and during mammalian development. A monoclonal antibody to human NRP1 was generated and validated for immunohistochemistry by western blotting, use of formalin-fixed cell pellets transfected with NRP1, immunofluorescence, and comparison with in situ hybridization. NRP1 expression was assessed in whole sections of 65 primary breast carcinomas, 95 primary colorectal adenocarcinomas, and 90 primary lung carcinomas. An additional 59 human metastases, 16 xenografts, and three genetically engineered mouse tumour models were also evaluated. Immunoreactivity for NRP1 was seen in vessels from normal tissues adjacent to cancer and in 98-100% of carcinomas. Tumour cell expression of NRP1 was also observed in 36% of primary lung carcinomas and 6% of primary breast carcinomas, but no colorectal adenocarcinomas. NRP1 was evaluated in mouse embryos, where expression was limited to the nervous system, endocardium, vascular smooth muscle, and, focally, endothelium on subsets of vessels. Moreover, in a model of VEGF-dependent angiogenesis in the postnatal mouse trachea, blockade of NRP1 signalling resulted in defective angiogenesis and recapitulated the effects of anti-VEGF treatment. These observations confirm NRP1 as a valid anti-angiogenic target in malignancy, and as a potential direct anti-tumour target in a subset of cancers. The data also confirm a role for NRP1 in physiological, VEGF-mediated angiogenesis.

Tying the knot: the cystine signature and molecular-recognition processes of the vascular endothelial growth factor family of angiogenic cytokines

The cystine-knot motif, made up of three intertwined disulfide bridges, is a unique feature of several toxins, cyclotides and growth factors, and occurs in a variety of species, including fungi, insects, molluscs and mammals. Growth factor molecules containing the cystine-knot motif serve as ligands for a diverse range of receptors and play an important role in extracellular signalling. This superfamily of polypeptides comprises several homodimeric and heterodimeric molecules that are central characters in both health and disease. Amongst these molecules are a group of proteins that belong to the vascular endothelial growth factor (VEGF) subfamily. The members of this family are known angiogenic factors that regulate processes leading to blood vessel formation in physiological and pathological conditions. The focus of the present review is on the structural characteristics of proteins that belong to the VEGF family and on signal-transduction pathways that become initiated via the VEGF receptors.

β-hairpin peptide that targets vascular endothelial growth factor (VEGF) receptors: design, NMR characterization, and biological activity

VEGF receptors have been the target of intense research aimed to develop molecules able to inhibit or stimulate angiogenesis. Based on the x-ray structure of the complex placental growth factor-VEGF receptor 1(D2), we designed a VEGF receptor-binding peptide reproducing the placental growth factor β-hairpin region Gln(87)-Val(100) that is involved in receptor recognition. A conformational analysis showed that the designed peptide adopts the expected fold in pure water. Moreover, a combination of NMR interaction analysis and cell binding studies were used to demonstrate that the peptide targets VEGF receptors. The VEGF receptor 1(D2)-interacting residues were characterized at the molecular level, and they correspond to the residues recognizing the placental growth factor sequence Gln(87)-Val(100). Finally, the peptide biological activity was characterized in vitro and in vivo, and it showed a VEGF-like behavior. Indeed, the peptide activated VEGF-dependent intracellular pathways, induced endothelial cell proliferation and rescue from apoptosis, and promoted angiogenesis in vivo. This compound is one of the few peptides known with proangiogenic activity, which makes it a candidate for the development of a novel peptide-based drug for medical applications in therapeutic angiogenesis.

Surface plasmon resonance biosensor for the detection of VEGFR-1--a protein marker of myelodysplastic syndromes

The surface plasmon resonance (SPR) biosensor system with dispersionless microfluidics for the direct and label-free detection of a soluble vascular endothelial growth factor receptor (sVEGFR-1) is described. The detection approach takes advantage of an affinity interaction between sVEGFR-1 and its ligand, vascular endothelial growth factor (VEGF-A), which is covalently immobilized on the surface of the SPR sensor. The ability of the immobilized VEGF-A to specifically bind the sVEGFR-1 receptor is demonstrated in a buffer. The detection of sVEGFR-1 in 2% human blood plasma is carried out by using the sequential injection approach. The detection limit of 25 ng/mL is achieved. In addition, we demonstrate that the functional surface of the sensor can be regenerated for repeated use.

Cytotoxicity of VEGF(121)/rGel on vascular endothelial cells resulting in inhibition of angiogenesis is mediated via VEGFR-2

Background

The fusion protein VEGF₁₂₁/rGel composed of the growth factor VEGF₁₂₁ and the plant toxin gelonin targets the tumor neovasculature and exerts impressive anti-vascular effects. We have previously shown that VEGF₁₂₁/rGel is cytotoxic to endothelial cells overexpressing VEGFR-2 but not to endothelial cells overexpressing VEGFR-1. In this study, we examined the basis for the specific toxicity of this construct and assessed its intracellular effects in vitro and in vivo.

Methods

We investigated the binding, cytotoxicity and internalization profile of VEGF₁₂₁/rGel on endothelial cells expressing VEGFR-1 or VEGFR-2, identified its effects on angiogenesis models in vitro and ex vivo, and explored its intracellular effects on a number of molecular pathways using microarray analysis.

Results

Incubation of PAE/VEGFR-2 and PAE/VEGFR-1 cells with ¹²⁵I-VEGF₁₂₁/rGel demonstrated binding specificity that was competed with unlabeled VEGF₁₂₁/rGel but not with unlabeled gelonin. Assessment of the effect of VEGF₁₂₁/rGel on blocking tube formation in vitro revealed a 100-fold difference in IC₅₀ levels between PAE/VEGFR-2 (1 nM) and PAE/VEGFR-1 (100 nM) cells. VEGF₁₂₁/rGel entered PAE/VEGFR-2 cells within one hour of treatment but was not detected in PAE/VEGFR-1 cells up to 24 hours after treatment. In vascularization studies using chicken chorioallantoic membranes, 1 nM VEGF₁₂₁/rGel completely inhibited bFGF-stimulated neovascular growth. The cytotoxic effects of VEGF₁₂₁/rGel were not apoptotic since treated cells were TUNEL-negative with no evidence of PARP cleavage or alteration in the protein levels of select apoptotic markers. Microarray analysis of VEGF₁₂₁/rGel-treated HUVECs revealed the upregulation of a unique "fingerprint" profile of 22 genes that control cell adhesion, apoptosis, transcription regulation, chemotaxis, and inflammatory response.

Conclusions

Taken together, these data confirm the selectivity of VEGF₁₂₁/rGel for VEGFR-2-overexpressing endothelial cells and represent the first analysis of genes governing intoxication of mammalian endothelial cells by a gelonin-based targeted therapeutic agent.

Antagonistic VEGF variants engineered to simultaneously bind to and inhibit VEGFR2 and alphavbeta3 integrin

Significant cross-talk exists between receptors that mediate angiogenesis, such as VEGF receptor-2 (VEGFR2) and α(v)β(3) integrin. Thus, agents that inhibit both receptors would have important therapeutic potential. Here, we used an antagonistic VEGF ligand as a molecular scaffold to engineer dual-specific proteins that bound to VEGFR2 and α(v)β(3) integrin with antibody-like affinities and inhibited angiogenic processes in vitro and in vivo. Mutations were introduced into a single-chain VEGF (scVEGF) ligand that retained VEGFR2 binding, but prevented receptor dimerization and activation. Yeast-displayed scVEGF mutant libraries were created and screened by high-throughput flow cytometric sorting to identify several variants that bound with high affinity to both VEGFR2 and α(v)β(3) integrin. These engineered scVEGF mutants were specific for α(v)β(3) integrin and did not bind to the related integrins α(v)β(5), α(iib)β(3), or α(5)β(1). In addition, surface plasmon resonance and cell binding assays showed that dual-specific scVEGF proteins can simultaneously engage both receptors. Compared to monospecific scVEGF mutants that bind VEGFR2 or α(v)β(3) integrin, dual-specific scVEGF proteins more strongly inhibited VEGF-mediated receptor phosphorylation, capillary tube formation, and proliferation of endothelial cells cultured on Matrigel or vitronectin-coated surfaces. Moreover, dual specificity conferred strong inhibition of VEGF-mediated blood vessel formation in Matrigel plugs in vivo, whereas monospecific scVEGF mutants that bind VEGFR2 or α(v)β(3) integrin were only marginally effective. Instead of relying on antibody associating domains or physical linkage, this work highlights an approach to creating dual-specific proteins where additional functionality is introduced into a protein ligand to complement its existing biological properties.

The VEGF family in cancer and antibody-based strategies for their inhibition

Angiogenesis is required in normal physiological processes, but is also involved in tumor growth, progression and metastasis. Vascular endothelial growth factor (VEGF), a primary mediator of angiogenesis in normal physiology and in disease, and other VEGF family members and their receptors provide targets that have been explored extensively for cancer therapy. Small molecule inhibitors and antibody/protein-based strategies that target the VEGF pathway have been studied in multiple types of cancer. This review will focus on VEGF pathway targeting antibodies that are currently being evaluated in pre-clinical and clinical studies.

Binding of ATP to vascular endothelial growth factor isoform VEGF-A165 is essential for inducing proliferation of human umbilical vein endothelial cells

BACKGROUND

ATP binding is essential for the bioactivity of several growth factors including nerve growth factor, fibroblast growth factor-2 and brain-derived neurotrophic factor. Vascular endothelial growth factor isoform 165 (VEGF-A(165)) induces the proliferation of human umbilical vein endothelial cells, however a dependence on ATP-binding is currently unknown. The aim of the present study was to determine if ATP binding is essential for the bioactivity of VEGF-A(165).

RESULTS

We found evidence that ATP binding to VEGF-A(165) induced a conformational change in the secondary structure of the growth factor. This binding appears to be significant at the biological level, as we found evidence that nanomolar levels of ATP (4-8 nm) are required for the VEGF-A(165)-induced proliferation of human umbilical vein endothelial cells. At these levels, purinergic signaling by ATP via P2 receptors can be excluded. Addition of alkaline phosphate to cell culture lowered the ATP concentration in the cell culture medium to 1.8 nM and inhibited cell proliferation.

CONCLUSIONS

We propose that proliferation of endothelial cells is induced by a VEGF-A(165)-ATP complex, rather than VEGF-A(165) alone.

Formation of VEGF isoform-specific spatial distributions governing angiogenesis: computational analysis

BACKGROUND

The spatial distribution of vascular endothelial growth factor A (VEGF) is an important mediator of vascular patterning. Previous experimental studies in the mouse hindbrain and retina have suggested that VEGF alternative splicing, which controls the ability of VEGF to bind to heparan sulfate proteoglycans (HSPGs) in the extracellular matrix (ECM), plays a key role in controlling VEGF diffusion and gradients in tissues. Conversely, proteolysis notably by matrix metalloproteinases (MMPs), plays a critical role in pathological situations by releasing matrix-sequestered VEGF and modulating angiogenesis. However, computational models have predicted that HSPG binding alone does not affect VEGF localization or gradients at steady state.

RESULTS

Using a 3D molecular-detailed reaction-diffusion model of VEGF ligand-receptor kinetics and transport, we test alternate models of VEGF transport in the extracellular environment surrounding an endothelial sprout. We show that differences in localization between VEGF isoforms, as observed experimentally in the mouse hindbrain, as well as the ability of proteases to redistribute VEGF in pathological situations, are consistent with a model where VEGF is endogenously cleared or degraded in an isoform-specific manner. We use our predictions of the VEGF distribution to quantify a tip cell's receptor binding and gradient sensing capacity. A novel prediction is that neuropilin-1, despite functioning as a coreceptor to VEGF₁₆₅-VEGFR2 binding, reduces the ability of a cell to gauge the relative steepness of the VEGF distribution. Comparing our model to available in vivo vascular patterning data suggests that vascular phenotypes are most consistently predicted at short range by the soluble fraction of the VEGF distributions, or at longer range by matrix-bound VEGF detected in a filopodia-dependent manner.

CONCLUSIONS

Isoform-specific VEGF degradation provides a possible explanation for numerous examples of isoform specificity in VEGF patterning and examples of proteases relocation of VEGF upon release.

TMEFF2 is a PDGF-AA binding protein with methylation-associated gene silencing in multiple cancer types including glioma

Background

TMEFF2 is a protein containing a single EGF-like domain and two follistatin-like modules. The biological function of TMEFF2 remains unclear with conflicting reports suggesting both a positive and a negative association between TMEFF2 expression and human cancers.

Methodology/Principal Findings

Here we report that the extracellular domain of TMEFF2 interacts with PDGF-AA. This interaction requires the amino terminal region of the extracellular domain containing the follistatin modules and cannot be mediated by the EGF-like domain alone. Furthermore, the extracellular domain of TMEFF2 interferes with PDGF-AA–stimulated fibroblast proliferation in a dose–dependent manner. TMEFF2 expression is downregulated in human brain cancers and is negatively correlated with PDGF-AA expression. Suppressed expression of TMEFF2 is associated with its hypermethylation in several human tumor types, including glioblastoma and cancers of ovarian, rectal, colon and lung origins. Analysis of glioma subtypes indicates that TMEFF2 hypermethylation and decreased expression are associated with a subset of non-Proneural gliomas that do not display CpG island methylator phentoype.

Conclusions/Significance

These data provide the first evidence that TMEFF2 can function to regulate PDGF signaling and that it is hypermethylated and downregulated in glioma and several other cancers, thereby suggesting an important role for this protein in the etiology of human cancers.

A fusion protein composed of receptor binding domain of vascular endothelial growth factor-A and constant region fragment of antibody: angiogenesis antagonistic activity

Vascular endothelial growth factor (VEGF) promotes the growth of solid tumor mainly via VEGF receptor-1 and receptor-2, which are expressed preferentially in proliferating endothelial cells. Therefore, a strategy for simultaneous blockage of both VEGF receptors may have a useful therapeutic effect in tumor growth. In this study, we utilized a fusion protein which is composed of receptor binding domain of VEGF-A (RBDV) and the constant region fragment (Fc) of a human immunoglobulin G1 (IgG1), to interfere with the growth of human umbilical vein endothelial cells (HUVECs) via VEGF receptors. The results showed that RBDV-IgG1 Fc was able to bind with both VEGF receptor-1 and receptor-2. In addition, RBDV-IgG1 Fc could decrease VEGF-induced proliferation and tube formation among HUVECs. Moreover, the cytotoxic test showed RBDV-IgG1 Fc could also enhance the cytotoxic activity of human natural killing cells. The data are suggesting that the fusion protein, RBDV-IgG1 Fc, may have potential as an angiogenesis antagonist for future tumor therapy.

Vascular endothelial growth factors and receptors: anti-angiogenic therapy in the treatment of cancer

Vascular endothelial growth factors (VEGFs) are critical regulators of vascular and lymphatic function during development, in health and in disease. There are five mammalian VEGF ligands and three VEGF receptor tyrosine kinases. In addition, several VEGF co-receptors that lack intrinsic catalytic activity, but that indirectly modulate the responsiveness to VEGF contribute to the final biological effect. This review describes the molecular features of VEGFs, VEGFRs and co-receptors with focus on their role in the treatment of cancer.

Engineered conformation-dependent VEGF peptide mimics are effective in inhibiting VEGF signaling pathways

Angiogenesis, or formation of new blood vessels, is crucial to cancer tumor growth. Tumor growth, progression, and metastasis are critically influenced by the production of the pro-angiogenic vascular endothelial growth factor (VEGF). Promising anti-angiogenic drugs are currently available; however, their susceptibilities to drug resistance and long term toxicity are serious impediments to their use, thus requiring the development of new therapeutic approaches for safe and effective angiogenic inhibitors. In this work, peptides were designed to mimic the VEGF-binding site to its receptor VEGFR-2. The VEGF conformational peptide mimic, VEGF-P3(CYC), included two artificial cysteine residues, which upon cyclization constrained the peptide in a loop native-like conformation to better mimic the anti-parallel structure of VEGF. The engineered cyclic VEGF mimic peptide demonstrated the highest affinity to VEGFR-2 by surface plasmon resonance assay. The VEGF peptide mimics were evaluated as inhibitors in several in vitro assays in which VEGF-dependent signaling pathways were observed. All VEGF mimics inhibited VEGFR-2 phosphorylation with VEGF-P3(CYC) showing the highest inhibitory effects when compared with unstructured peptides. Additionally, we show in several angiogenic in vitro assays that all the VEGF mimics inhibited endothelial cell proliferation, migration, and network formation with the conformational VEGF-P3 (CYC) being the best. The VEGF-P3(CYC) also caused a significant delay in tumor development in a transgenic model of VEGF(+/-)Neu2-5(+/-). These results indicate that the structure-based design is important for the development of this peptidomimetic and for its anti-angiogenic effects.

Exogenous administration of vascular endothelial growth factor prior to human respiratory syncytial virus a2 infection reduces pulmonary pathology in neonatal lambs and alters epithelial innate immune responses

Human respiratory syncytial virus (RSV) affects thousands of children every year. Vascular endothelial growth factor (VEGF) is a regulator of vasculogenesis, pulmonary maturation, and immunity. In order to test the extent to which VEGF may alter RSV infection, 4 groups of lambs received either human recombinant VEGF (rhVEGF) or phosphate-buffered saline (PBS) pretreatment followed by inoculation with human RSV strain A2 or sterile medium. Lambs in each group were sacrificed at 2, 4, and 6 days post infection. Expression of surfactant protein-A (SP-A), surfactant protein-D (SP-D), sheep β-defensin-1 (SBD-1), tumor necrosis factor α (TNFα), interleukin (IL)-6, IL-8, interferon β, and endogenous VEGF were measured to determine effect of rhVEGF pretreatment. RSV lambs pretreated with rhVEGF had reduced viral mRNA and decreased pulmonary pathology at day 6. Pretreatment with rhVEGF increased mRNA expression of SP-A, SBD-1, and TNFα, with alteration of expression in RSV lambs. Endogenous VEGF mRNA levels were increased at day 2 regardless of pretreatment. Pretreatment with rhVEGF increased pulmonary cellular proliferation in RSV lambs at day 4 post infection. Overall, these results suggest that pretreatment with rhVEGF protein may have therapeutic potential to decrease RSV viral load, decrease pulmonary lesion severity, and alter both epithelial innate immune responses and epithelial cell proliferation.

Positron emission tomography tracers for imaging angiogenesis

Position emission tomography imaging of angiogenesis may provide non-invasive insights into the corresponding molecular processes and may be applied for individualized treatment planning of antiangiogenic therapies. At the moment, most strategies are focusing on the development of radiolabelled proteins and antibody formats targeting VEGF and its receptor or the ED-B domain of a fibronectin isoform as well as radiolabelled matrix metalloproteinase inhibitors or alpha(v)beta(3) integrin antagonists. Great efforts are being made to develop suitable tracers for different target structures. All of the major strategies focusing on the development of radiolabelled compounds for use with positron emission tomography are summarized in this review. However, because the most intensive work is concentrated on the development of radiolabelled RGD peptides for imaging alpha(v)beta(3) expression, which has successfully made its way from bench to bedside, these developments are especially emphasized.

Structural insights into the binding of vascular endothelial growth factor-B by VEGFR-1(D2): recognition and specificity

The formation of blood vessels (angiogenesis) is a highly orchestrated sequence of events involving crucial receptor-ligand interactions. Angiogenesis is critical for physiological processes such as development, wound healing, reproduction, tissue regeneration, and remodeling. It also plays a major role in sustaining tumor progression and chronic inflammation. Vascular endothelial growth factor (VEGF)-B, a member of the VEGF family of angiogenic growth factors, effects blood vessel formation by binding to a tyrosine kinase receptor, VEGFR-1. There is growing evidence of the important role played by VEGF-B in physiological and pathological vasculogenesis. Development of VEGF-B antagonists, which inhibit the interaction of this molecule with its cognate receptor, would be important for the treatment of pathologies associated specifically with this growth factor. In this study, we present the crystal structure of the complex of VEGF-B with domain 2 of VEGFR-1 at 2.7 A resolution. Our analysis reveals that each molecule of the ligand engages two receptor molecules using two symmetrical binding sites. Based on these interactions, we identify the receptor-binding determinants on VEGF-B and shed light on the differences in specificity towards VEGFR-1 among the different VEGF homologs.

Biochemical and structural analysis of the binding determinants of a vascular endothelial growth factor receptor peptidic antagonist

Cyclic peptide antagonist c[YYDEGLEE]-NH(2), which disrupts the interaction between vascular endothelial growth factor (VEGF) and its receptors (VEGFRs), represents a promising tool in the fight against cancer and age-related macular degeneration. Furthermore, coupled to a cyclen derivative, this ligand could be used as a medicinal imaging agent. Nevertheless, before generating such molecular probes, some preliminary studies need to be undertaken in order to define the more suitable positions for introduction of the cyclen macrocycle. Through an Ala-scan study on this peptide, we identified its binding motif, and an NMR study highlights its binding sites on the VEGFR-1D2 Ig-like domain. Guided by the structural relationship results deduced from the effect of the peptides on endothelial cells, new peptides were synthesized and grafted on beads. Used in a pull-down assay, these new peptides trap the VEGFRs, thus confirming that the identified amino acid positions are suitable for further derivatization.

Molecular interaction studies of vascular endothelial growth factor with RNA aptamers

With widespread applications in biosensors, diagnostics and therapeutics, unraveling the mechanism of the interactions between aptamers and their targets has become extremely important. In this study, the interaction forces between an aptamer and its protein target were successfully measured via AFM-based force spectroscopy at the molecular level. The angiogenic protein, vascular endothelial growth factor (VEGF(165)) covalently tethered to a mixed self-assembled monolayer surface and an anti-VEGF(165) aptamer attached to an AFM cantilever was used to probe this interaction. By comparing the binding probability and the force distribution of this system in a series of experiments, the interaction between the aptamer and the protein was confirmed and the effect of loading rate on the rupture force was studied. The specificity of the aptamer was investigated by measuring interactions with VEGF(121), an isoform of VEGF missing a critical binding domain, and VEGF(165) isoform blocked with heparin. The lower frequency of binding events compared with that of VEGF(165) reflected that despite a high affinity to its preferential target, the selectivity of this aptamer is impaired to some extent due to the flexible structure of aptamers. By changing the concentration of Mg(2+) ion in the binding buffer, we could verify the effect of metal ions as stabilizers of aptamer conformation. The results provide evidence at the molecular level that the structural stability of aptamer is closely related to higher binding force and that rigid aptamer tertiary structures require higher forces to unbind the aptamer/protein complex.

Evolution of viviparity and uterine angiogenesis: vascular endothelial growth factor (VEGF) in oviparous and viviparous skinks

During pregnancy, uterine vasculature of live-bearing lizards proliferates to support embryonic growth and development. Vascular endothelial growth factor (VEGF) is the most potent of a suite of growth factors responsible for uterine vascularization in mammals. We have sequenced VEGF mRNA transcripts expressed in the uterus of oviparous and viviparous Australian skinks, and compared uterine VEGF expression in nonreproductive and late-reproductive Saiphos equalis, a fossorial viviparous skink. VEGF sequences differed between phylogenetic groups of skinks, rather than oviparous and viviparous skinks. Two transcripts were identified in the uterus of each species that had the same splice sites as human VEGF(165) and VEGF(189). A third transcript, found only in uterine and testis tissue from S. equalis, had the same splice sites as human VEGF(111). This is the first natural expression of VEGF(111), previously found only in human cultured cells subjected to environmental stress. All the three VEGF transcripts identified showed higher expression in uterus from late-reproductive S. equalis than nonreproductive females. The different angiogenic properties of VEGF transcripts provide a mechanism that may produce the variety of placental complexities observed in viviparous skinks. The presence of VEGF(111) in S. equalis may be an opportunity to investigate the function of this unique transcript in a whole animal system.